This invention relates to a control system for a direct injection engine of spark ignition type mounted in an automotive vehicle or the like.
A control system is disclosed, for example, in Japanese Examined Patent Publication NO. 5-83730. This system is for an stratified charge engine provided with fuel feeders for supplying fuel into combustion chambers to control an output corresponding to a load, ignition devices provided in the combustion chambers, a throttle for controlling an open area of an intake passage without mechanically linking it with an accelerating operation, a catalyst provided in an exhaust passage, an exhaust gas temperature detector for detecting a temperature of an exhaust system, wherein a stratified combustion is carried out by supplying fuel by means of the fuel feeders in such a manner that the fuel is present around the ignition devices for ignition and a lean combustion is carried out by increasing the open area of the intake passage in proportion to the amount of fuel by means of the throttle at least at low engine loads, whereas a uniform combustion is carried out by feeding the fuel into the combustion chambers in a dispersed manner for ignition at high engine loads. This control system is constructed such that the temperature of the catalyst is increased at an earlier stage while suppressing undercooling of the catalyst by reducing the open area of the intake passage by means of the throttle to reduce an amount of intake air when an output of the exhaust gas temperature detector indicates that the temperature of the exhaust system has fallen to or below a set value.
The above construction in which the amount of intake air is reduced by narrowing the intake passage by the throttle when the exhaust gas temperature is low has an advantage that undercooling of the catalyst for purifying the exhaust gas can be suppressed by preventing a fall of the exhaust gas temperature through admission of a larger amount of intake air into the combustion chambers. However, this construction has a problem that deterioration of combustibility is unavoidable if a control is executed to reduce the amount of intake air in a stratified combustion region since an air-fuel mixture around electrodes of a sparking plug tend to be excessively enriched.
More specifically, in the stratified combustion region of the engine, a pumping loss has been conventionally reduced by increasing an opening of a throttle valve to a larger extent than necessary in order to provide an engine output required according to an operating condition. Particularly, in an idle operating condition where a small amount of intake air is required to provide an engine output, since the opening of the throttle valve can be excessively increased beyond a value corresponding to a necessary amount of intake air, there is an advantage that a pumping loss can be significantly reduced while maintaining combustibility at a proper level by setting an amount of fuel to be sprayed and a fuel injection timing such that a stratus of air-fuel mixture of a proper concentration is formed around the electrodes of the sparking plug. However, if the amount of intake air is reduced by controlling the throttle valve in order to suppress undercooling of the exhaust gas purifying catalyst in the idle operating condition of the engine, it is an unavoidable problem that the air-fuel mixture present around the electrodes of the sparking plug is excessively enriched.
It is an object of the present invention to provide a control system for a direct injection engine of spark ignition type which is free from the problems residing in the prior art.
According to an aspect of the invention, a control system for a direct injection engine of spark ignition type which is provided with an exhaust gas purifying catalyst provided in an exhaust passage, a fuel injection valve for directly spraying fuel into a combustion chamber, a sparking plug having an electrode projecting into the combustion chamber, the control system comprises an intake air amount controller for controlling the amount of intake air to be admitted into the combustion chamber, and a fuel injection controller for carrying out stratified combustion in a stratified combustion region set in a low engine load region when the engine is warm while carrying out uniform combustion in a uniform combustion region set in the high engine load region. When the intake air amount controller executes the control to reduce the amount of intake air in the stratified combustion region when the engine is warm, the fuel injection controller advances the fuel injection starting timing within the compression stroke and sets a degree of advancement in such a range where the stratified combustion of the engine can be maintained.
Accordingly, stratified combustion can be maintained when the control to reduce the amount of intake air in the stratified combustion region is executed in order to, for example, prevent a fall in exhaust gas temperature, thereby advantageously maintaining combustibility at a satisfactory level while preventing the air-fuel ratio from decreasing.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments/examples with reference to the accompanying drawings.